The present invention relates to a vehicle orientation calculating device used in a navigation system mounted on a vehicle, in which the position or the orientation of the vehicle, map information of the neighborhood thereof, etc. are displayed.
In a prior art navigation system mounted on a vehicle, as indicated e.g. in JP-A-58-70117, the position and the orientation of the vehicle as well as a trajectory of drive were obtained by means of an angular velocity sensor and a velocity sensor, the trajectory of drive being compared with map data, and the position and the orientation of the vehicle were corrected on a route in the map data so that the trajectory of drive was in accordance with the map data, to be displayed on a display screen.
However the prior art navigation device mounted on a vehicle had a problem that, in the case where there was no chance to correct the position or the orientation over a long distance, e.g. when it was driven on a road, which was not inscribed in a map, errors, were accumulated in the position or the orientation of the vehicle thus calculated so that precise position and orientation of the vehicle were lost.
In order to solve this problem, there was known a method, by which the position of the vehicle was corrected by adding a device for calculating a real position by using external information such as GPS (Global Positioning System), as indicated e.g. in JP-A-63-177016, thereto. However, since GPS had only position information, it has a problem that it was not possible to correct the orientation of the vehicle.